Method and apparatus for agglomerating finely divided solid material



Jan. 22, 1957 l. H. WYNNE METHOD AND APPARATUS FOR AGGLOMERATING FINELY DIVIDED SOLID MATERIAL. Filed March 27, 1952 3 Sheetsheet l INVENTOR.

[9A A. W/NNE ATMRNE ys Jan. 22, 1957 l. H. WYNNE 2,773,055

METHOD AND APPARATUS FOR AGGLOMERATING FINELY DIVIDED SOLID MATERIAL Filed March 27, 1952 3 Sheets-Sheet 2 fie. 2

INVEN TOR. [m4 h. W NNE A r TOENE' 1957 l. H. WYNNE 2,778,056

METHOD AND APPARATUS FOR AGGLOMERATING FINELY DIVIDED SOLID MATERIAL Filed March 27, 1952 3 Sheets-Sheet 5 IN V EN TOR.

Ari-01? United States Patent Q Application March 27, 1952, Serial No. 278,777

12 Claims. (Cl. 18-1) This invention relates to a method and apparatus for use in agglomerating finely divided solid material and, more particularly, to a procedure and apparatus for forming such material into pellets or balls.

It is frequently necessary to agglomerate finely divided material into larger size particles or pellets. For example, iron ore concentrates, fine dust, and the like, cannot be utilized as a substantial part of the charge of a blast furnace until they have been formed intolumps or pellets many times the size of the individual particlesthereof. One convenient mode of agglomeratin-g or pelletizing. materials of this nature is to roll or tumble them in a drum or cylinder while in a moist state, thereby forming ball-like bodies which, in the case of ore concentrates or the like, may be subsequently hardened by heating. In conventional apparatus and procedures of this nature,

however, ditficulties have been encountered in attempting to produce balls of desired size and having the requisite strength for the necessary handling preceding the hardening operation.

An object of this invention is to provide an improved method and apparatus for forming ball-like bodies from finely divided material, and, while not limited thereto,

is especially useful for agglomerating fine ore particles; such as iron ore concentrates or the like, into pellets or balls of desired diameter and having sufficient strength prior to hardening to withstand handling such as sizing by screening and transportation by conveyors.

Another object of the invention is to provide an improved method and apparatus for forming ball-like bodies from finely divided material characterized by the introduction of the material into the interior of a rotating cylindrical member having its axis disposed substantially horizontally and the inner surface thereof formed with helical grooves so that the said material is subjected to' complex rolling and/or tumbling motions with the result that the material is formed into compact ball-like bodies.

A further object of the invention is to provide a method and apparatus for forming and maintaining the aforementioned grooved surface on the interior of the cylindrical member.

An additional object of the invention is to provide an improved apparatus for forming ball-like bodies comprising a rotating cylindrical member or drum disposed in a substantially horizontal position and provided with a helical scraper with the said cylinder and scraper revolving in opposite directions at different speeds so that a part of the material to be formed into balls-adheres to the inner wall of the cylinder and is scraped into sub-- stantially helical grooves While the remaining material rolls and/or tumbles thereover in a complex motion productive of compact ball-like bodies. p r

The invention also has as an object thereof the pr vision of a method and apparatus for forming ball-like bodies from finely divided material as defined above and in which the formed bodies are accelerated towards the discharge end of the cylindrical member in which theyare formed.

a The invention further resides in certain novel steps of procedure and in the combination and arrangement of parts of the apparatus, and hence further objects and advantages of the invention will be apparent to those skilled in the art to which it pertains from the following description of the present preferred embodiment, described with reference to the accompanying'drawings in which:

Fig. 1 is a longitudinal sectional view taken through the present preferred embodiment of a balling apparatus constructed in accordance with thisinvention and capable of performing the method thereof, certain parts of the apparatus being shown in elevation and others broken away for the sake of clarity of illustration.

Fig. 2 is a top plan view of the balling apparatus shown in Fig.1. 7

Fig. 3 is an end elevational view of the inlet end of the balling drum or cylinder as seen from the right-hand side of Figs. 1 and 2; and

Fig. 4 is a fragmentary, enlarged, sectional view taken through a portion of the side wall of the balling cylinder or drum substantiallyon the line 4-4 of Fig. l and illustrating the novel nature of the interior surface of the apparatus. a i

';The apparatus of this invention, and'which is employed in performing the novel method of agglomerating' flanged wheels such as 13 and 14, see Figs. 1 and 3.

The tracks 11 and 12 may be in the form of I-beams or other structural members having cross sections similar to railroad rails while the pairs of wheels 13 and 14 are preferably flanged similar to the wheels employed upon the trucks of railroad vehicles. The pairs of wheels I 13 and 14 are disposed so that each of the individual wheels of a pair thereof is at either side of the vertical center line of the cylinder or drum, thereby providing a cradle-like support.

Endwise movement of the drum or cylinder 10 may be prevented by oppositely disposing the flanges of the pairs of wheels 13 and 14, but, as herein shown, a more positive'prevention of such endwise movement is provided bya pair of thrust rollers or wheels 15 and 16,

positioned to engage opposite sides of one of the rail or track members such :as 12. As shown in Fig. 1, these thrust rollers or wheels 15 and 16 are rotatably supported on suitable bearings or brackets, such as 17 and 18, with the axes of the rollers approximately vertical.

The bearings for the flanged wheels 13, 14 and the bracket or bearing members 17, 18 are mounted upon suitably interconnected structural steel members to provide a base frame, generally designated 19, which is in turn supported upon a floor or structural members, generally designated 20. As mentioned heretofore, the axis of the cylindrical member or drum 10 is disposed substantially horizontally but this axis may be tilted slightly from the horizontal by any suitable means. For example,

.such tilting of the cylinder or drum may be eifected by raising one end of the base frame 19 relative to the supporting structure or floor 20. As indicated in Fig. l, the forward or left-hand portion of the baseframe 19 is bolted to the floor or supporting means 20,'as indicated at 5 21, while the rear or right-hand portion of the frame a chain 48 to a sprocket wheel 49, see Figs. 2 and 3. The sprocket wheel 49 is connected at one end of a shaft 50 which extends substantially parallel with the axis of the cylinder or drum and is suitably supported upon the frame members which support the drum. The other end of the shaft 50 is provided with asprocket wheel 51 which is connected by a chain 52 to a sprocket wheel 53 carried by or connected with the shaft on which the drum driving gear 25 is supported.

It will be apparent from the construction just described that the direction of rotation of the cylinder or drum 10 is reverse to that of the shaft 40 for the scraping means. Moreover, the sizes of the sprocketwheels are such that an increase of speed of the scraping means relative to that of the drum is provided and the relative speeds of the drum and scraping means, once determined, are maintained due to the positive drive provided by the sprocket wheels, chains and gears. Hence, variation of the speed of the motor 26 not only varies the speed of the drum or cylinder 10 but also correspondingly varies the speed of the scraping means 39. Preferably, the direction of rotation of the cylindrical member or drum 10 is counterclockwise, as viewed from the entrance end of the drum as seen in Fig. 3, while the direction of rotation of the scraping means is clockwise when viewed from the same location. These directions are, of course, reversed when the drum is viewed from the discharge end.

The position of the helical scraping means is so located that the convolutions thereof cut helical grooves in the layer of material adhering to the expanded metal or the.

like on the interior of the cylinder or drum. In the preferred constmction, the shaft of the scraping means is disposed to the right of the vertical centenline of the cylinder or drum 10, as viewed from the inletend, and on a plane extending at an angle of 45 degrees upon the horizontal central plane through the drum. The diameter of the scraping means and the position of its shaft 40 along the aforementioned inclined plane-are'such that the bottoms of the grooves cut in the material adhering to the side wall of the drum do notqextend to the expanded metal or the like 38 which is provided on the interior of the drum, see Fig. 4.

- Due to the aforementioned directions of relative rotation of the scraping means 39 and of the cylindrical member or drum 10, and also because of the hand of.the convolutions of the several portions of the scraping means,

helical grooves having configurations substantially similar" to those shown in Fig. 1 will be formed during rotation of the drum and scraper. From this figure it will be seen that the major portion of the cylindrical member ordrum has the grooves therein sloping downwardly to the right, that is, back towards the inlet end of the drum, while the grooves 55 adjacent the discharge end, as well as the grooves 56 immediately adjacent the inlet, slope in the opposite direction. Moreover, the regions intermediate the grooves 54 and the grooves 55, 56, where the direction of slope changes, are in the form of single circumferentially extending grooves 57 and 58. The surface thus formed within the cylindrical member may be protected,

from decrescence or deterioration by spraying the latter with waterglass or other material of similar nature, although this is not always necessary since the grooves are continuously re-defined during operation of the mechanism through the relative rotation of the drumand scraper.

After the grooved surface has been formed .within the balling cylinder or drum if), additional finely divided material introduced therein by the conveyor 29 will receive a complex rolling and/ or tumbling movement which results in the formation of well compacted ball-like bodies of superior quality. The sizes of these bodies may be controlled by the speed of rotation of the drum, the moisture content of the material, and the inclination of the axis of the drum or cylinder 10. During this rolling and/or tumbling operation, the material forms first into relatively small nuclei or balls which are carried partly aroundwithin the cylindrical member or drum" bythe aforementioned grooves. A part of this material tends to roll or slide downwardly within said grooves and hence be carried back towards the entrance of the drum while other portions of the material tend to adhere within the' said grooves. Any such adheringmaterial reaching the scraping means 39 will be crushed and/or scraped back' into the drum for further rolling action. In general, the material will be carried partly around within the drum during its rotation, roll backwardly through the said grooves a part of the distance and then dropped-over the outer edges into the next succeeding groove or grooves,

thus progressing forwardly within the drum towards the discharge end, this progression being assisted, if necessary, by slightly inclining the axis of the drum or cylinder 10 towards the discharge end. The aforementioned tendtogether with the movement of the bodies over the'suc cessive edges or ridges between the grooves provides an extremely compact form of the ball-like bodies vsov that by the time they. have reached the discharge endv of thedrum they are generally in suitable form for transfer to' an indurating furnace or other means of hardening and/or further treating the bodies.

As the ball-like bodies approach the discharge 'end ofthe cylindrical member or drum they enter the portion of this member which has the helical grooves 55 sloping in the opposite direction from the grooves 54 of the main body of the drum with the result that the bodies are accelerated intheir movement toward the discharge end of the drum, thus facilitating their transfer therefrom and preventing injury thereto by continued rotation within the drum and striking against other bodies. which may be of a size less than that desired is removed from the material discharging from the drum by a screening means 59 which is substantially frusto-conical in shape and is formed by spaced 'angularly disposed rods 60 of stainless steel or the like welded to a reinforcing ring or rings such as 61, thereby providing a unitary structure which is bolted or otherwise secured to the cylinder or drum 10 adjacent the discharge end. The inclination of the separate rods or bars of the screening means is in the same general direction as that of the grooves 55 thereby facilitating discharge of the bodies.

The material thus discharged from the cylindrical member or drum 10 is therefore classified according to size by the screening means 59 with the bodies equal to or larger than the selected size, corresponding to the openings in the screen, being transferred to a further treatment while the bodies and fragments thereof of lesser size fall through the openings between the bars 60 of the screening means and are conveyed by suitable means back to the entrance to the balling drum. This separate disposal of the product from the cylindrical member or drum may be effected by separate conveyors, but in the form shown in the drawings a single conveyor 62 is provided which is of the belt type having an integral rib or ridge 63 extending longitudinally therealong substantially medially so as to provide, in effect, two separate compartments. The said ridge or dividing portion 63 is disposed substantially under the outer edge of the screening means 59 so that the ball-like bodies of size equal to or greater sized bodies and fragments thereof drop upon a portion of the conveyor to the right of the said ridge. A suitable stop or diverting member 64 may be provided in front of the discharge end of the drum to prevent the ball-like bodies from being impelled beyond the edge of the conveyor 63. This stop means may comprise a vertically extending plate faced with flexible material, the lower end of which rides upon the upper surface of the conveyor 62.

Any material cmagoso.

The discharge end of the conveyor 62 is positioned? over 'two oppositely running conveyor-s65 and fidso tha't' the ball lile bodies of" proper size are deposited upon oneconveyor; such as 65; for' travel to a suitablehardening funn-acesor the lilie; while the bodies-'and fragmentsthereof of: smallersize drop upon the conveyordb and are carried in-th'e opposite diteetionback, by meansnotshown; to the entrance: of. the balling drum for re-circul'ation there-= through It should be-noted; however, that by virtue of the novel construction and method of balling heredis closed that quantity 'ofmateriahneeded to be re-circul'ated istconsiderably less than that provid'ed' by prior structures;

- As. has: been mentioned heretofore; thehelicallgrooves 56v adjacent the: inlet portion: of: the: balling cylinder'or' drum have an inclination: or slope-reverse to the' grooves- 547- in the main portion of the drum; This assists in' directing thematerial awayfrom=the end p'late 36 and into themaim portion K of the cylindrical memberor: drum, thus not:' onlyprevent-ing leakage: of thematerial.- from the: inlet end but also; providing distribution ofthe material as 'iti is initiall y chargedinto thecylinder'by the conveyor 299 In -addition to theformihg-of helical grooves bythe scraper portion 45b; the outer end of this part of the scraping means may be shaped as indicated at 6'? to provide'. a. scraping action upon the adjacent inner-face of the end plate- 35, thus: reducing thetendency of the-finely divided material to work out of the cylindrical memberon d'rum along the shaft 40.

Theangle of the helical grooves 54,- as measured fromatve'ntically extending. line, may be varied by varying the relative speed of the balling drum with-respect to the speed of theflhelical scraping means. This may be effected by changing the sprocket 53 in the drive for the scraping means. Any change of this; or of the other sprocket wheels: which would result in a different relative speed between the drum-and'thescraping means will, of course, alten thegrooves within the drum, and itwill therefore be-necessary torun the apparatus for asuflicient period of time to form the new grooves by cutting through the ridgesbetween the previous grooves and building up the newridges defining the new grooves. Therefore; where it appears that it may be necessary to change the angle of the helical grooves, it is preferable not to-harden the surface after formation of the grooves to the extent that itiwould be difficult to alter by simply allowing the scraping means to out new grooves. angularity of the grooves is to remainfixed'for anappreciable length of time, the interior surface can be proteoted from decrescence to a greater extent, and in such instances it is even possible to form this helical surface of materials other than the material which isto be formed ample to illustrate the nature of the grooved surfaces formed'iwithin the balling drum. Thus, a drum having aadiameter of 7 feet may be provided on its inner surface withiexpauded metal after which finely divided moist iron ore-concentrates, or other similar material which will adhereato' the surface of the expanded metal'andform a continuousilayer thereon are introduced; The scraping means-for such -a-cylinder ordrum has the'scraper portions-onribbon-like members 14" in diameter and of a 14f pitch-throughout, but with the convolutions of the twoiendhportionsreversely disposed relative tothose of thermainportion. This scraping'meaus'is positioned so thatlthe depth of the grooves formed is in the order of %3! andl'the thickness of the materialin the depth of the groovesalikewisein the order'of' When such a drum iserotated at ten. revolutions a minute and the scraping meaus is rotated at 56% revolutions per minute, the helicalangle ofthefgrooves-is 17 7'. At thesame speed of the. drum. but 4 with tthe'scraper rotating at-83Va revolutionsper minute, the helicalangleis. 24 22. Thedis: tance between ridges of' the grooves is then in the order Where, however, the

8 of. 4l67'". one speedzofawylinder or drum of: this-charactenmay besvariedbetween 8a and. Lfirevol'utions: per'minute, if: it is d-esiredi to) alter the. rate oh theformation: of, ther' ball-like: bodies and/or. the size thereof. Thespeeds of the. scraper means: 39 will, of course; vary. from those given above as the. speed: of the drum is varied, but the relationship (ah-the speeds will remain in the same order so that the configuration oh the helical grooves withini the drum is not altered except by changing the sprocket. wheel 53% assmentioned heretofore.

It is believed thatthe; operation: of the apparatus and? the manner'in which the method is'performed will now be clearly apparent from: the. foregoing detailed description-r However, it is desiredto emphasize that when: the grooved surface is formed" of: the finely divided ma-- terial from which theballt-like bodies are formedthe said grooved surface i's'continuously maintained? by the: actiom of the helical scraper-upon the material continuously supplied to the. cylinder or'drum; However, this surface may be protected against decrescence by spraying with: a suitable hinder or adhesive and in. some instances the: surface canbe formed of materials other than those? which are to be'agglomerated'.

Although the method and apparatus of this invention have been illustrated and described in considerable detail: as they are incorporated in a preferred embodiment, it will be understood that variations may be made in thestructures'andini the steps of the procedure by those skilled in the art-after having had the advantages'of this disclosure; Thus; thedimensions given for the drum and scraper may'bevariedfrom the values stated. Move'--- over; the grooved surface may in some instances be formed by scraping means other thantthe helical momber shown; Als'o; in some instances, the cylinder or drum with thenovel grooved surface may be employed to elfe'ct' agglomeration without the need of a powerdriven scraper especiallywhere the "grooved surface is sufficiently' protected: from decrescence' due to wearing away by abrasion, cracking, or other'deterioration.

The above and other variations and adaptations of the invention-are deemed properly encompassed within the ambit thereof and, consequently, the detailed description andillustrationsof this application are not to be considered as limitations upon the invention except as may be required by the spirit and scope of the subjoined claims.

Having thus described the invention, I claim:

1. The method of producing ball-like bodies from finely divided material comprising introducing the material in a moist condition into-the interior of a hollow rotating cylindrical member disposed with its axis extending substantially horizontally so that the said material tends to'adhere to-the inner surface of the cylindrical member as a continuous layer thereabout, scraping the said layer'of material with a helical member rotating at a speed greater than" the speed of the cylindrical member and in the opposite direction, thereby producing a helically grooved surface ofmultiple convolutious in the'material adhering to the said cylindrical member, and continuing the introduction of thefinely divided material into one end of said cylindrical member while rotating; the latter and-said helical member at the aforementioned relative speeds so-that the said finely divided materia'l' receivesa-complex rolling'act'ion upon said surface re sultiug'in the formation of ball-like bodies which roll. towards the other end of said cylindrical member.

2. The method of producing ball-like bodies from" finely divided material comprising introducing thev material in a moist condition into one end of a hollow cylindrical member disposed with its axis extending substantially horizontally so that the said material isdistributedlengthwise off saidmember and adheres tothe inner surfaceofthe cylindrical member as a continuous layerthereahout, scraping the said layertof material-with.-

a helical'member rotating at a speed greater than the speed of the cylindrical member and in the opposite direction with the hand of the helical member being such that it produces a helically grooved surface of multiple convolutions in the material adhering to the said cylindrical member with the grooves thereof sloping towards the end at which the finely divided material is introduced, and continuing the introduction of said material while rotating the cylindrical member and said helical scraping member at the aforementioned relative speeds so that the said finely divided material receives a complex rolling action upon said surface resulting in the formation of ball-like bodies which roll towards the end of said cylindrical member opposite that into which the material was introduced.

3. The method asdefined in claim 2 and further comprising accelerating the discharge of the formed bodies from the said cylindrical member by providing the said grooves in the inner surface thereof adjacent the discharge end with a slope in the opposite direction to that of the slope of said grooves intermediate the ends of the cylindrical member.

4. The method of producing ball-like bodies from finely divided material comprising introducing a quantity of the material in a moist condition into the interior of a hollow rotating cylinder disposed with its axis extending substantially horizontally so that the said material tends to adhere to the inner surface of the cylinder as a continuous layer thereabout, scraping the said layer of material with a helical member rotating at a speed greater than the speed of the cylinder and in the opposite direction thereby producing a helically grooved surface of multiple convolutions in the material adhering to the said cylinder, spraying the said grooved surface with a substance preventing decrescence of the said surface, and thereafter introducing further quantities of the finely divided material into one end of said cylinder while rotating the latter and said helical scraping member at the aforementioned speeds so that the said finely divided material receives a complex rolling action upon said surface resulting in the formation of ball-like bodies which roll towards the other end of said cylinder.

5. The method of producing ball-like bodies from finely divided material comprising introducing a quantity of the material in a moist condition into the interior of a hollow rotating cylinder disposed with its axis extending substantially horizontally so that the said material tends to adhere to the inner surface of the cylinder as a continuous layer thereabout, scraping the said layer of material with a helical member rotating at a speed greater than the speed of the cylinder and in the opposite direction with the hand of the helical member being such that it produces a helically grooved surface of multiple convolutions in the material adhering to the said cylinder with the majority of the grooves thereof sloping towards one end of the cylinder, spraying the said grooved surface with a substance preventing decrescence of the said surface, and thereafter introducing further quantities of the finely divided material into one end of said cylinder while rotating the latter and said helical scraping member at the aforementioned relative speeds so that the said finely divided material receives a complex rolling action upon said surface resulting in the formation of ball-like bodies which roll towards the other end of said cylinder.

6. An apparatus of the character described for producing ball-like bodies from finely divided material comprising a hollow cylinder rotatably supported with its axis extending substantially horizontally, means adjacent one end of said cylinder to introduce finely divided material into the interior thereof, means to rotate said cylinder, a helical scraping means rotatably supported adjacent the inner surface of said cylinder and adapted to engage and scrape material adhering to the said inner surface, and means to rotate said scraping means in a reverse direction to that of the cylinder rotation and at a faster speed than the speed of the cylinder thereby producing helical 10'? grooves in the'materialx adhering to the interior of the cylinder, wherebythe finely divided material not adhering to the cylinder has a complex rolling motion im parted thereto resulting in production of ball-like bodies which are discharged fromthe other end of said cylinder.

7. An apparatus as defined in claim 6 wherein the convolutions of the said helical scraping means adjacent either end thereof are reversed relative to'the convolutions intermediate the ends. p

8. An apparatus as defined in claim 6 wherein the said cylinder and scraping means are rotated by a common source of power with a positive driving means between said cylinder and scraping means to thereby maintain a predetermined timed relationship of their speeds of rotation.

9. An apparatus of the character described for producing ball-like bodies from finely divided material comprising a drum rotatably supported with its axis extending substantially horizontall means adjacent one end of said drum to introduce finely divided material into the interior thereof, means to rotate said drum, a helical scraping means extending through said drum adjacent the inner surface of the latter and adapted to engage and scrape material adhering to the said inner surface, means. externally of said drum rotatably supporting said scraping means, positive drive means interconnecting the said scraping means and drum rotating means to effect rotation of the scraping means in reverse direction to that of the drum rotation and at a faster speed than the speed of the latter thereby producing helical grooves in the material adhering to the interior of the drum, whereby the finely divided material not adhering to the drum has a complex rolling motion imparted thereto resulting in production of ball like bodies which are discharged from the end of the drum opposite that into which the material was initially introduced.

10. An apparatus as defined in claim 9 wherein the convolutions of the said helical scraping means adjacent either end thereof are reversed relative to the convolutions intermediate the ends, and the convolutions intermediate the ends of the scraping means have a hand such that they produce grooves which slope towards the end of the drum into which the material is introduced While the reversed convolutions form grooves adjacent the ends of the drum which slope towards the discharge end of the latter.

11. The method of producing a surface for the formation of ball-like bodies from finely divided material comprising introducing a portion of the finely divided material in a moist condition into the interior of a hollow rotating cylindrical member disposed with its axis extending substantially horizontally so that the said 7 material tends to adhere to the inner surface of the member as a continuous layer thereabout, and scraping the said layer in a manner producing a plurality of helical grooves substantially throughout the length of said layer and sloping towards the entrance end of said cylindrical member, whereby the continued introduction of finely divided material into the entrance end of said cylindrical memher while rotating the latter and continuing the said scraping action results in the additionally introduced material receiving a complex rolling action upon the grooved surface thereby forming ball-like bodies.

12. The method of producing a surface for the formation of ball-like bodies from finelydivided material comprising introducing a portion of the finely divided material in a moist condition into the interior of a hollow rotating cylindrical member disposed with its axis extending substantially horizontally so that the said material tends to adhere to the inner surface of the cylindrical member as a continuous layer thereabout, scraping the said layer of material with a helical member rotating at a speed greater than the speed of the cylindrical member and in the opposite direction thereby producing a helically 76 grooved surface of multiple convolutions in the material memes agihaenjng: w the said eylindricah member, cantn'nuing the, introducfinm at the: finely dividedv matefiak inm one end; Oi said cylindrical; mambe: while rotating the latter: andl saidahelfim'l member at the 'afierememioned. relative speeds,,whmeby apart; of the; additionally inflmducei matenial maintains the said gmmexi surface anch the remainder wgerbhen with. the: maflezi'al; detached from said surfaee neneiwes a. eemplexe rolling: antion upom saidi sum face thereby forming ball-like bodies.

Refierences; Cited in the; file of this patent STATES, PATENTS Stone July 2, 1-925 Tiers Oct. 1 8, 1932 Fasting New 6,v 193,4 Ray Jan. 14, 1936 Calling Aug.. 7, 1945 Firth Dec. 3,. 1946 Skoog June 24, 1947 Dick Feb. 3, 194B 

